1. Field of the Invention
The invention relates to a process for treating a steel surface.
2. Description of the Related Art
Such a treatment is intended to bring about passivation of the corrosion-susceptible surfaces of steel containers, chemical reactors, pipes, distillation columns, steel supports, etc. In particular, the invention relates to the passivation of surfaces in chemical plants or plant components which come into contact simultaneously with residual moisture, chlorine, hydrogen chloride [P. M. Bhadha, E. R. Greece: Joule-Thomson Expansion and Corrosion in HCl Systems in Solid State Technology July 1992 pp. 3-7], chlorosilanes, hydrogen and reactive elemental silicon.
It is known that residual moisture in gases and/or stainless steel plants causes corrosion in the presence of hydrogen chloride [J. Y. P. Mui: Corrosion Mechanism of Metals and Alloys in the Silicon-Hydrogen-Chlorosilane System at 500 C in Corrosion—NACE, 41(2), 1985 pp. 63-69; W. C. Breneman: Direct Synthesis of Chlorosilanes and Silane in Catalyzed Direct Reactions of Silicon, Elsevier 1993 pp. 441-457, in particular table 3 on p. 454].
A natural corrosion protection on the surface of carbon steel or of stainless steel can be formed at above 500° C. in the reductive atmosphere of a chlorosilane-hydrogen chloride-hydrogen mixture. This also applies to SiC-coated carbon steel.
In stainless steel containers, the steel is usually tested for chloride stress cracking corrosion.
Hydrogen chloride chlorinates phosphorus-containing constituents of the steel alloy [H. Viefhaus, B. Richarz: Phosphor in Eisen and Stahl in Materials and Corrosion, 46, 1995 pp. 306-316], as a result of which phosphorus chlorides are formed and these either contaminate, as volatile contamination, the silane stream or can react with silanes or boron compounds to form undefined adducts which cannot be separated from the products in the purification of chlorosilanes by distillation [Xiao Ji-mei, Shen Hua-sheng: The Theoretical Aspects of Preventing Corrosion of Stainless Steel . . . in the Production of Polycrystalline Silicon in Xiyou-jinshu—Rare Metals, Chin. Vol 1-2, 1982 pp. 3-15, in particular equation (44) and pp. 13-15].
In the reductive hydrogen atmosphere of a deposition of polycrystalline silicon (Siemens process U.S. Pat. No. 7,708,970 B2; chlorosilane and hydrogen as starting materials), phosphorus chlorides are reduced and phosphorus is preferentially incorporated into the deposited polycrystalline silicon.
Passivation of the steel surface can slow or prevent both the moisture and the reductive corrosion.
It is known from JP7090288 A2 and U.S. Pat. No. 2,985,677 A that silicon-organic halogen compounds are chemisorptively bound as silyl esters to active Fe—OH sites on steel surfaces, so that they can be used as oil-free lubricants in the working of steel sheets.
JP8010703 A2 discloses polysiloxanes from the hydrolysis and condensation of organic chlorosilanes as primers for corrosion protection constituents and as corrosion protection resins.
DE 3920297 A1 describes heteropolycondensates of siloxy-aluminate esters with organosilanes bearing hydrolyzable radicals, optionally with addition of organofunctional silanes with silicic esters, as corrosion protection. The corrosion protection is in this case brought about by dipping into a silanization bath and subsequent drying. Drying is carried out at at least 50° C.